This invention relates to a recording device for picking up an image and converting the image to a digital picture data, and more particularly relates to a technique suitable for preventing the alteration of a digital picture data and improvement of the reliability of the digital image data as an evidence.
Heretofore, digital cameras and other recording devices in which an optical image formed by use of a lens is converted to an electric signal by use of an image pick-up element such as CCD (Charge Coupled Device) and the obtained picture data is recorded digitally have been known. Recently, with the improvement in performance of the image pick-up element, it is possible to obtain the picture quality equivalent to that of silver halide photography, therefore it will be expected that the digital camera is employed for image pick-up for various certification and evidence instead of the ordinary camera.
The digital picture data is characterized in that it is easily edited and duplicated by use of a computer. In the case that a digital camera is used for image pick-up for various certification or evidences, such alteration and evidence can be altered more elaborately in comparison with those derived from an ordinary camera.
For example, it could happen that a digital picture data on another person obtained by use of a digital camera is duplicated without consent and is used for various certification or evidence, otherwise an digital picture data obtained by use of a digital camera which is edited to change the original picture and is used for various certification or evidence. In this case, it is not easy to detect the alteration in comparison with the silver halide photography obtained by an ordinary camera.
The present invention was accomplished to solve the above-mentioned problem, it is the object of the present invention to provide a digital camera and another recording device which are suitable for preventing the alteration of an obtained digital picture data and improvement of the reliability of a digital picture data as an evidence.
To solve the above-mentioned problem, the first aspect of the present invention provides a recording device for picking up an image and converting the image to digital picture data comprising; a digital signature means for generating a digital signature of the digital picture data, and a storing means for adding the digital signature to the digital picture data and storing the digital picture data having the added digital signature in a storage medium.
An authentication means for authenticating the digital picture data by use of the digital signature added to the digital picture data may be additionally provided.
As the digital signature technique used for the digital signature means and the authentication means of the present aspect, for example, a technique described in T. Elgamal, xe2x80x9cA Public Key Cryptosystem and a Signature Scheme Based on Discrete Logarithmsxe2x80x9d (IEEE Trans. on Inform. Theory, Vol. IT31, No. 4, pp 469-472, 1985) has been known. In detail, the digital signature means evaluates the digital picture data by use of hash function, which is one-way function, the evaluation result namely a hash value is encrypted by use of a private key (signature key) in accordance with the public key cryptography system to thereby generate a digital signature of the digital picture data. On the other hand, the authentication means obtains a hash value by decrypting the digital signature added to the digital picture data by use of the public key (verification key) which is the one component of the paired private key, and compares this hash value with the hash value obtained by evaluating the digital picture data by use of the hash function. In the case that both hash values are identical, the digital picture data is regarded as a digital picture data which has not been subjected to alteration after generation of the digital signature, and authenticated.
According to the present aspect, because the digital picture data, which has been obtained by picking up an image, having the added digital signature of the data is stored in a storage medium, alteration which is added to the data after generation of the digital signature is detected by authentication by use of the digital signature. Because a digital signature is generated in the recording device during image picking up, the fraudulence such as alteration of the digital picture data is detected easily in the situation that the digital picture data is used for various certification and evidence.
The second aspect of the present invention provides a recording device for picking up an image and converting the image to digital picture data comprising; a digital watermarking means for embedding a related information on the digital picture data in the digital picture data by means of the digital watermarking technique, and a storage means for storing the digital picture data in which the related information has been embedded.
Wherein, a related information getting means for extracting the related information embedded in the digital picture data by means of the digital watermarking technique may be additionally provided. The term xe2x80x9cdigital watermarking techniquexe2x80x9d denotes a technique in which a predetermined information is embedded in a digital picture data according to a predetermined rule, for example, the luminance information on the digital picture data is changed so that the predetermined information can not be extracted from the digital picture data at least without using the predetermined rule. In one technique the original digital picture data (the digital picture data before embedding of the predetermined information) is referred, and in the other technique the original digital picture data is not referred, when the predetermined information is extracted from the digital picture data. The technique in which the related information can be extracted from the digital picture data without referring to the original data is preferably used for the related information getting means of the present aspect. As this type of technique, for example, a technique described in S. Shimizu et al., xe2x80x9cData Hiding based on neighbor pixels statisticsxe2x80x94reliabilityxe2x80x94xe2x80x9d (In Proc. of IPSJ 56th annual conference, 1998) has been known.
According to the present aspect, because the digital picture data obtained by picking up an image having the embedded related information on the data, for example, the copyright information such as pick-up date, photographer and place where the image is picked up, is stored, the related information is extracted from the digital picture data and the content can be confirmed. Because the related information is embedded in the recording device during image pick-up, the recording device is used for image picking up for various certification and evidence to improve the reliability of the digital picture data as an evidence.
In the present aspect, the digital watermarking means which divides the digital picture data into a plurality of areas, embeds the related information on the digital picture data in at least one area from among the plurality of divided areas, and integrates the plurality of divided areas including the area in which the related information has been embedded to generate the digital picture data in which the related information has been embedded may be used.
By structuring the digital watermarking means as described herein above, the related information is embedded in an arbitrary area of the digital picture data divided into the plurality of areas, therefore the work area and the load on the CPU used for embedding the related information is reduced in comparison with the case in which the related information is embedded in the whole digital picture data. This effect is particularly advantageous for the recording device because the small size and light weight are desirable.
In the case that the deterioration of the picture quality of the area is apprehensive as the result that all the related information is embedded concentratedly in the area, the process may be modified as described herein under. In detail, the related information is divided into a plurality of segments so that each segment corresponds to the plurality of respective areas. The plurality of corresponding respective segments are embedded in the plurality of respective areas successively, and then the plurality of areas in which the corresponding segments of the related information has been embedded are integrated to generate the digital picture data having the embedded related information.
The third aspect of the present invention provides a recording device for picking up an image and converting the image to digital picture data comprising;
a digital watermarking means for embedding an related information on the digital picture data in the digital picture data by means of the digital watermarking technique,
a digital signature means for generating a digital signature of the digital picture data in which the related information has been embedded, and
a storage means for adding the digital signature to the digital picture data in which the related information has been embedded and storing the resultant digital picture data in a storage medium.
Wherein, the recording device may additionally comprise an authentication means for authenticating the digital picture data in which the related information has been embedded by use of the digital signature added to the digital picture data in which the related information has been embedded, and a related information getting means for extracting the related information embedded in the digital picture data by means of digital watermarking technique.
According to the present aspect, because the related information on the data is embedded in the digital picture data obtained by picking up an image and furthermore the digital signature of the data is added to the digital picture data having the embedded related information and then it is stored in a storage medium, alteration added after generation of the digital signature is detected by authentication by use of the digital signature, and the related information is extracted from the data to confirm the content. Accordingly, the recording device is used for picking up an image for various certification and evidence, as the result the fraudulence such as alteration of the digital picture data is detected and the reliability of the digital picture data as an evidence is improved.
In the present aspect, the recording device may additionally comprise a compressing means for compressing the digital picture data in which the related information has been embedded, the digital signature means generates a digital signature of the compressed data, and the storage means adds the digital signature to the compressed data and stores the resultant compressed data in a storage medium.
Otherwise, the recording device may additionally comprise a compressing means for compressing the digital picture data, the digital watermarking means embeds the related information on the digital picture data in the digital picture data by means of the digital watermarking technique, the digital signature means generates a digital signature of the compressed data in which the related information has been embedded, and the storage means adds the digital signature on the compressed data in which the related information has been embedded, and stores the resultant compressed data in a storage medium.
By structuring as described herein above, the amount of information to be stored in the storage medium is reduced in both cases. In the former case the related information is embedded in the digital picture data and then the data is compressed, on the other hand in the latter case the digital picture data is compressed and then the related information is embedded, as the result, the former case is more advantageous than the latter case in that the adverse effect of the related information on the original digital picture data is less severe.